全文获取类型
收费全文 | 232692篇 |
免费 | 2247篇 |
国内免费 | 799篇 |
专业分类
化学 | 116766篇 |
晶体学 | 3996篇 |
力学 | 10757篇 |
综合类 | 1篇 |
数学 | 25503篇 |
物理学 | 78715篇 |
出版年
2020年 | 1787篇 |
2019年 | 2043篇 |
2018年 | 2719篇 |
2017年 | 2651篇 |
2016年 | 3912篇 |
2015年 | 2389篇 |
2014年 | 3967篇 |
2013年 | 10072篇 |
2012年 | 7528篇 |
2011年 | 9392篇 |
2010年 | 6684篇 |
2009年 | 6628篇 |
2008年 | 8701篇 |
2007年 | 8733篇 |
2006年 | 8271篇 |
2005年 | 7491篇 |
2004年 | 6917篇 |
2003年 | 6111篇 |
2002年 | 6060篇 |
2001年 | 7090篇 |
2000年 | 5372篇 |
1999年 | 4235篇 |
1998年 | 3563篇 |
1997年 | 3472篇 |
1996年 | 3293篇 |
1995年 | 3008篇 |
1994年 | 2951篇 |
1993年 | 3042篇 |
1992年 | 3151篇 |
1991年 | 3332篇 |
1990年 | 3084篇 |
1989年 | 3027篇 |
1988年 | 3066篇 |
1987年 | 2955篇 |
1986年 | 2800篇 |
1985年 | 3808篇 |
1984年 | 4005篇 |
1983年 | 3198篇 |
1982年 | 3410篇 |
1981年 | 3336篇 |
1980年 | 3230篇 |
1979年 | 3335篇 |
1978年 | 3422篇 |
1977年 | 3350篇 |
1976年 | 3448篇 |
1975年 | 3141篇 |
1974年 | 3150篇 |
1973年 | 3194篇 |
1972年 | 2235篇 |
1971年 | 1849篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
P. Thomsen-Schmidt K. Hasche G. Ulm K. Herrmann M. Krumrey G. Ade J. Stümpel I. Busch S. Schädlich A. Schindler W. Frank D. Hirsch M. Procop U. Beck 《Applied Physics A: Materials Science & Processing》2004,78(5):645-649
High-accuracy film thickness measurements in the range below 100 nm can be made by various complex methods like spectral ellipsometry (SE), scanning force microscopy (SFM), grazing incidence X-ray reflectometry (GIXR), or X-ray fluorescence analysis (XRF). The measurement results achieved with these methods are based on different interactions between the film and the probe. A key question in nanotechnology is how to achieve consistent results on a level of uncertainty below one nanometre with different techniques.Two different types of thickness standards are realised. Metal film standards for X-ray techniques in the thickness range 10 to 50 nm are calibrated by GIXR with monochromatised synchrotron radiation of 8048 eV. The results obtained at four different facilities show excellent agreement. SiO2 on Si standards for SE and SFM in the thickness range 6 to 1000 nm are calibrated by GIXR with monochromatised synchrotron radiation of 1841 eV and with a metrological SFM. Consistent results within the combined uncertainties are obtained with the two methods. Surfaces and interfaces of both types of standards are additionally investigated by transmission electron microscopy (TEM). PACS 61.10.Kw; 68.55.Jk; 06.20.Fn; 06.60.Mr; 07.79.Lh 相似文献
972.
Emrys A. Jones Nicholas P. Lockyer John C. Vickerman 《International journal of mass spectrometry》2007,260(2-3):146
Recent developments in desorption/ionisation mass spectrometry techniques have made their application to biological analysis a realistic and successful proposition. Developments in primary ion source technology, mainly through the advent of polyatomic ion beams, have meant that the technique of secondary ion mass spectrometry (SIMS) can now access the depths of information required to allow biological imaging to be a viable option.Here the role of the primary ion C60+ is assessed with regard to molecular imaging of lipids and pharmaceuticals within tissue sections. High secondary ion yields and low surface damage accumulation are demonstrated on both model and real biological samples, indicating the high secondary ion efficiency afforded to the analyst by this primary ion when compared to other cluster ion beams used in imaging. The newly developed 40 keV C60+ ion source allows the beam to be focused such that high resolution imaging is demonstrated on a tissue sample, and the greater yields allow the molecular signal from the drug raclopride to be imaged within tissue section following in vivo dosing.The localisation shown for this drug alludes to issues regarding the chemical environment affecting the ionisation probability of the molecule; the importance of this effect is demonstrated with model systems and the possibility of using laser post-ionisation as a method for reducing this consequence of bio-sample complexity is demonstrated and discussed. 相似文献
973.
P.A. Kuzmin 《Journal of Mathematical Analysis and Applications》2007,330(1):744-750
This note is devoted to construction of the domain of the regular representation of Diff+(S1). We consider a subgroup of diffeomorphism group such that the Malliavin-Shavgulidze measure is quasi-invariant with respect to the left action of the subgroup. The measure appears to be quasi-invariant with respect to the left action of diffeomorphisms with discontinuous second derivative. We derive an expression for quasi-invariance density and obtain an additional PSL(2,R) symmetry breaking term. 相似文献
974.
The coupling of visible nanosecond laser pulses to metallic targets irradiated in vacuum is studied. The expressions of the vapour and plasma ignition times are obtained. Two cases for vapour breakdown in the plasma ignition process are considered. The first case is that 40 generations of new electrons are born in vapour generation time before plasma formation as assumed in the literature. The second case is that 10 generations of new electrons are born in vapour generation time. Molybdenum (Mo), niobium (Nb) and aluminium (Al) targets are considered for illustrations of our results. The expression of the plasma ignition time for the Al target is substantially different from that reported in the literature. The vapour and plasma ignition threshold laser intensities are calculated and compared with those reported in the literature. Reasons for disagreement are discussed. The plasma ignition threshold estimated in the second case is noted to be in good agreement with the reported experimental result. 相似文献
975.
976.
We propose general variational inclusion problems which are slightly different from corresponding problems considered in several recent papers in the literature and show that they are advantageous. Sufficient conditions for the solution existence are established. As applications we derive consequences for several special cases of variational inclusion problems, quasioptimization problems, equilibrium problems and implicit variational inequalities and show that they improve the results of some recent existing papers. 相似文献
977.
978.
979.
N. P. Kobelev 《Physics of the Solid State》2002,44(1):195-198
The relaxation contribution of the molecular reorientation in an elastic field of an acoustic wave to the effective shear moduli is calculated in the framework of the phenomenological two-level model of orientational states in the low-temperature phase of solid C60. The polarity of the rotation axis of C60 molecules and the possible existence of orientational domains in the structure of the low-temperature phase are taken into consideration. The estimates obtained are compared with the available experimental data. 相似文献
980.
Y. D. Kolekar S. B. Kulkarni Keka Chakraborty A. Das S. K. Paranjpe P. B. Joshi 《Pramana》2004,63(2):189-197
Nd2Sn2O7 pyrochlores with the substitution of Zr4+ were prepared by conventional ceramic double sintering technique. The single-phase formation was confirmed by X-ray diffraction
and neutron diffraction techniques. Relative intensity calculations for X-ray diffraction analysis were performed for oxygen
positional parametersx = 0.331 and 0.375, while Rietveld refinements were employed for neutron diffraction data. The neutron diffraction study revealed
that there are only two anion sites with 48f and 8b positions. This indicates that the 8a site, i.e. O(3) sublattice, is completely
vacant and the structure is a perfect cubic pyrochlore with space group Fd3m (O
h
7
). From the conductivity measurements, it is observed that the electronic conductivity dominates from room temperature up
to about 525 K and forT > 525 K, the oxygen ion conduction dominates the charge transport in these compositions. Complex impedance spectroscopy indicates
the existence of grain and grain boundary as two separate elements. 相似文献